Catalytic dehydrogenation of aliphatic amines to nitriles, imines, or vinylamines and dealkylation of tertiary aliphatic amines over halide cluster catalysts of group 5 and 6 transition metals

A molybdenum halide cluster, (H3O)2[(Mo6Cl8)Cl6] ⋅ 6H2O, with an octahedral metal framework was used as a catalyst in a gas-flow reactor under hydrogen or helium. Diethylamine started to react above 300 °C, and dehydrogenation to N-ethylideneethylamine proceeded selectively above 350 °C. Dibutylamine yielded the corresponding dehydrogenation product, and pyrrolidine and piperidine were dehydrogenated to 1-pyrroline and 2,3,4,5-tetrahydropyridine. Dehydrogenation of primary amines yielded the corresponding nitriles and the condensation product N-alkylidenealkylamine. Tripropylamine and tributylamine were dehydrogenated to yield, for the most part, N-vinyldialkylamines. In contrast, triethylamine was dealkylated to diethylamine. Thus, the halide cluster exhibited a characteristic catalysis for aliphatic amines: nitrogen-bonded hydrogens were removed completely to yield nitrile or imine, and when there was no such hydrogen, a neighboring hydrogen or the nitrogen-bonded alkyl group was removed. Niobium, tantalum, and tungsten chloride clusters of the same metal framework were also active catalysts for dealkylation and dehydrogenation of diethylamine.